This invention relates to a valve which delays the release of brakes, and more particularly, to such a valve for use in a system for effecting automatic disengagement of a transmission upon the application of the brakes, and reengagement of the transmission upon release of the brakes.
In conventional loader vehicles, an engine is employed to power the vehicle for movement from place to place and also to provide power, often through hydraulic pumps, to raise and manipulate a bucket or other implement carried by the vehicle. It has been recognized as desirable to employ a system which provides a connection between the service brakes and the transmission of the vehicle to neutralize the transmission automatically upon actuation of the brakes. This has the advantage of freeing the hands of the operator to manipulate the bucket controls, instead of actuating a transmission or clutch lever, and also insures availability of the full power of the engine for manipulating the bucket without delay.
A disadvantage of many prior devices for this purpose is that a brief period occurs in which a clutch or transmission remains disengaged after the brakes are released, due to the difference between the time required to reengage the transmission and the time required to release the brakes. This makes it difficult to properly position the implement and may present a dangerous situation, particularly when operating on a slope, because the vehicle is momentarily free to coast.
The systems disclosed in U.S. Pat. No. 3,050,165 to Day et al, and U.S. Pat. No. 3,181,667 to Lohbauer et al provide systems which include means for delaying the release of the brakes thereof until the transmission is reengaged. Such metering techniques as disclosed therein have been found acceptable in a system wherein a relatively large amount of fluid is returned upon the release of the brakes, i.e., for example, when the system utilizes drum-type brakes. However, with vehicles using brake systems which return a relatively small amount of fluid upon the release of the brakes, i.e., for example in vehicles using caliper disc-type brakes, such small amounts of fluid returned from the brakes results in the fact that the systems of such two patents do not reliably control the delay properly to insure full engagement of the transmission.
U.S. Pat. No. 3,583,422 to Dach et al, and U.S. Pat. No. 3,626,968 to Hancock disclose brake valves which delay the application of the brakes, but allow relatively free release thereof. Thus, these patents are cited as of general interest.